We are studying the genetic organization of polyoma virus and the influence of viral gene products on cell growth regulation. We have characterized three T-antigens encoded in the early region of the polyoma genome. We plan to study the control of expression of these T-antigens in polyoma-infected and transformed cells, and the effect of each of the proteins on cell growth properties. We will try to define the location of each of the T-antigens in infected and transformed cells, and test possible functions of the proteins, using polyoma mutants defective or conditional for transformation.